/Engine/Source/Runtime/CoreUObject/Public/AssetRegistry/AssetData.h
Returns true if this is the main asset in a package, true for maps and assets but false for secondary objects like class redirectors Every UAsset is also a TopLevelAsset. Specifically, this is just testing whether the asset name matches the package name, and it is possible for legacy content to not return true for any asset in a package.
bool IsUAsset() const